Step switch

ABSTRACT

The invention relates to a load selector for step switches in step transformers with two movable selector contacts. A suitable vacuum switch is located downstream of the first movable selector contact to switch the load current and a suitable switch for switching the compensation current is located downstream of the second movable selector contact. Both of the selector contacts are independently movable in such a way that one of the selector contacts moves slowly and the other selector contact rapidly moves or jumps between positions. The sequence of operation of the selector contacts is independent of the switching direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national phase of PCT applicationPCT/EP93/01112 filed 6 May 1993 with a claim to the priority of Germanpatent applications P 42 23 439.5 filed 16 Jul. 1992, P 42 37 231.3filed 4 Nov. 1992, and P 42 32 165 also filed 4 Nov. 1992 (and all nowissued as German patents).

FIELD OF THE INVENTION

The invention relates to a step switch for step transformers with twomovable selector contacts.

BACKGROUND OF THE INVENTION

In such a known step switch as described in German patent document2,321,369 there are two selector arms each carrying a respectiveselector contact, the first of the movable selector contacts beingconnected to a vacuum switch intended for continuous-currenttransmission and interruption and the second of the movable selectorcontacts being connected to a vacuum switch and series-connected shuntresistor intended only for conducting and interrupting the compensatingcurrent. The two movable selector contacts are connected to each otherand to the vacuum switch so that when the switching direction changesthe rotation direction of the drive also changes and during eachindexing of the second selector contact the vacuum switch that isintended only to conduct and interrupt the compensating current inseries with the shunt resistor is left connected momentarily all aloneto the tap at high voltage. With this known step switch according to theswitching direction the resistance contact either leads or trails; theswitching procedure is different depending on switching direction.

As a result both of the arms carrying the respective selector contactsmust be jointly actuated by the energy-storage unit; this isparticularly disadvantage due to the complex kinematics as well as themechanically costly energy-storage unit which is required in particularby the different switching steps depending on switching direction.

OBJECT OF THE INVENTION

It is therefore an object of the invention to provide a step switchwhose kinematics are very simple and which requires for actuating theswitching means an energy-storage unit that is uncomplicated and thatworks the same in both directions with the same switching steps.

SUMMARY OF THE INVENTION

A step switch is used with a step transformer having a row of contactsincluding at least a first contact and an adjacent second contact. Thestep switch has a threaded drive shaft extending along the row oftransformer contacts, a support movable relative to the drive shaftalong the row of transformer contacts and threaded on the drive shaft,and a fixed contact fixed on the support and movable therewith along therow of transformer contacts to successively engage same. A bussconductor extending longitudinally along the row of transformer contactsis connected via a vacuum switch to the fixed contact. The shaft isrotated in one sense to slowly displace the support in one directionalong the row for displacement of the fixed contact from the firstcontact to the second contact and in the opposite direction along therow for displacement of the fixed contact slowly in the oppositedirection from the second contact to the first contact. A slide movablerelative to the drive shaft and to the support carries a movable contactand a switch and a resistor are connected between the movable contactand the buss conductor. A spring-loaded force-storage unit is bracedbetween the slide and the support for, on movement of the fixed contactfrom the first contact to the second contact, rapidly displacing themovable contact from the first contact to the second contact once thefixed contact is moved fully to the second contact and on oppositemovement of the support by the shaft for, on movement of the fixedcontact from the second contact to the first contact, rapidly displacingthe movable contact from the second contact to the first contact oncethe fixed contact is moved to the first contact.

It is a particular advantage of the step switch according to theinvention that--independent of the switching direction and therefore ofthe rotation direction of the drive--the auxiliary contact always leadsand thus must only be actuated slowly, the particular advantage beingthat the step switch is directly actuated by the drive shaft. The energystorage unit therefore only actuates the always trailing main contact sothat a particularly simple energy-storage unit results.

With the step switch according to the invention the main and auxiliarycontacts are completely independently movable: The auxiliary contact iscontinuously moved by the slowly rotating drive shaft and in effectselects the new to be switched transformer tap while the main contact ismade to follow with a jump by the energy-storage unit.

In a further advantageous embodiment of the invention the main andauxiliary contacts are vertically separate from each other and pivotalabout a common axis independently of each other and the fixed contacts,which are concentric to this axis, which are each connected with a tapof the step winding, extend vertically so far that the main and also theauxiliary contacts can slide over them.

While it is known from German published application 2,219,220 to providefixed contacts that contact rollers can slide over in several verticalplanes this known arrangement serves mainly to improve the spatialrelationships as several coupled-together rollers roll over them.

According to a further advantageous embodiment of the invention it isalso possible to arrange the fixed contacts in a straight row as inslide switches and to form the movable contacts so that even in thiscase they can slide unhindered over them. This can be done by making thefixed contact U-shaped so that the adjacent contact rollers or blades orthe like that are next to each other can slide over them.

It is particularly advantageous, in order to increase resistance tofailure, to connect in series with the vacuum switch which continuouslypasses the voltage of the first movable selector contact a similarvacuum switch and to actuate these two vacuum switches generally at thesame time.

It is also possible to mount all the switching elements on one of themovable contacts and to provide only an electrical connection to theother movable switching contact.

BRIEF DESCRIPTION OF THE DRAWING

The invention is more closely described by way of example below withreference to drawings.

FIG. 1 is a first step switch according to the invention in a schematicview;

FIG. 2 shows the necessary switching steps of this first step switch onswitching from one transformer tap to another;

FIG. 3 is the corresponding switching diagram of this first step switchwhen switching from n to (n+1), then to (n+2), and finally then back to(n+1);

FIG. 4 shows a different form of this step switch with all elementsmounted on a movable arm which here carries the main contact SKM;

FIG. 5 is a second embodiment of a step switch according to theinvention in a schematic representation;

FIG. 6 is shows a third embodiment of a step switch according to theinvention in a schematic representation;

FIG. 7 shows the switching diagram of the third step switch again for aswitching from n to (n+1), then to (n+2), and finally back to (n+1);

FIG. 8 again shows a different form of this third step switch where allelements are again mounted on a movable arm which here carries the maincontact SKM;

FIG. 9 shows in top view the construction of a step switch schematicallyshown in FIG. 8;

FIG. 10 also shows this step switch in a side view in plane X--X of FIG.9;

FIG. 11 is the same step switch in a side view in plane X1--X1 of FIG.9;

FIG. 12 is an individual driven part in a partly perspectiverepresentation;

FIG. 13 also shows the switching scheme of this step switch;

FIG. 14 shows an individual fixed contact all alone in perspective view;and

FIG. 15 shows such a fixed contact together with the two independentlymovable selector contacts that bridge it and that are formed as acontact bridge.

SPECIFIC DESCRIPTION

In the schematic diagram of FIG. 1 taps of the step winding of a steptransformer are connected with fixed contacts n, (n+1), . . . , (n+m)which can be arranged in a circle or straight line. The step switch alsohas a switching contact SKM which is connected via a vacuum switch SKVwith the common conductor and an auxiliary contact HKW that isindependent therefrom and movable without a mechanical connection andwhich is connected in series through an auxiliary switch HKM and a shuntresistor R to the same conductor.

FIG. 2 shows the necessary switching steps. These switching steps arethe same if the switching is going from a lower to a higher voltagelevel or oppositely. The individual switching steps are shown at 1through 9.

FIG. 3 shows the switching diagram for a multiple step switching from nto (n+1), then to (n+2) and then back to (n+1).

It is clear that regardless if one is switching to a higher or lowervoltage level the auxiliary contact HKW always leads and carries out apreselection. Meanwhile the fixed contacts n, (n+1), (n+2), are soconstructed that they can be switched independently from each other andfrom the auxiliary contact HKW.

FIG. 4 schematically illustrates a variation on such a step switch whereall the elements are mounted on a movable arm AR which here carries themain contact SKM and this arm AR, which is shown in dot-dash lines, isconnected with the conductor. The auxiliary contact HKW which is onceagain independently movable is insulated and is electrically connectedwith the arm AR carrying the main contact SKM.

FIG. 5 shows another embodiment wherein the mechanical auxiliary switchHKM is replaced by another vacuum switch HKV.

FIG. 6 shows a further embodiment of a step switch where the movableswitch contact SKM is connected in series through two vacuum switchesSKV and ZKV to the conductor. Such an arrangement provides much greatersecurity with respect to failure of a vacuum switch in the load line.

FIG. 7 again shows the corresponding switching diagram with a switchingfrom n to (n+1), then to (n+2), and then back again to (n+1).

FIG. 8 shows a step switch according to FIG. 6 in a variant with all theswitch elements mounted on a movable arm AR which here carries the maincontact SKM. The auxiliary contact HKW that is movable independentlythereof is again insulatedly mounted and connected electrically with thearm AR carrying the main contact SKM.

FIG. 9 shows the construction of a step switch according to FIG. 8 fromabove, FIG. 10 shows this same step switch from the side in the planeA--A, and FIG. 11 in the plane B--B.

The step switch comprises a housing 1 on whose end wall are verticallyarranged the step contacts 2 which each are formed of two contact parts2.1 and 2.2 which extend parallel to each other into the interior of thestep switch. A threaded spindle 4 of a drive 3 projects downward intothe housing 1. The side of the housing 1 opposite the fixed stepcontacts 2 carries two cam rails 5, two guide rails 6, and a conductorrail 7 whose functions are described more closely below. The step switchfurther has a spring-type energy-storage unit which is formed of atubular slide 8 which is surrounded by a compression spring 9 which inits turn surrounds the threaded spindle 4 that drives it. The slide 8supports on insulation a preselecting auxiliary contact 10 which passesover or engages a contact part 2.1 of the selected fixed contact 2 andis fixed to a vertically extending release cam 20. The spring-typeenergy-storage unit further is comprised of a generally U-shaped drivenpart 11. Integrally fixed on the driven part 11 to follow thesnap-action movement of same when released are a switching contact 12which switches respective further contact parts of each fixed stepcontact 2, three vacuum switches 13, 14, and 28, a conductive contactbar 15, further rollers 24 and 25, as well as two-armed levers 26, 27,and 29 for actuating the vacuum switches 13, 14, and 28, as well as acontact blade 18 that is in contact with the conductor bar 7, andfinally at least one shunt resistor 19.

For switching the threaded spindle 4 rotates and moves the surroundingtubular slide 8 continuously upward or downward, depending on rotationdirection. This compresses the spring 9 which is braced against an upperabutment 9.1 or a lower abutment 9.2; the spring-energy unit is loaded.

During this movement of the slide 8 relative to the still stationarydriven part 11 a roller 21 of a release slide bolt 22 of the driven part11 rides along the also vertically moving cam 20 which has ramps 20.1and 20.2.

Simultaneously the preselecting auxiliary contact 10 fixed viainsulation on the slide 8 moves; it leaves the original fixed stepcontact 2 and reaches the next fixed contact positioned above or below.With its other end the preselecting auxiliary contact 10 rides on thecontact rail 15 which is connected at least over a shunt resistor 19with the vacuum cell 13. Subsequently the roller 21 comes to therespective ramp 20.1 or 20.2; the release lever 22 is shiftedhorizontally out of the stop 23 in the guide rail 6 and the entiredriven part 11 jumps after the slide 8. At the same time the guide rail6 assumes the function of mechanical vertical guiding.

The switching contact 12 now also leaves the previous fixed contact 2and gets to a contact part of the new step contact whose other contactpart is already engaged by the auxiliary contact 10. The auxiliarycontact 10 is connected via the contact rail 15 through the seriescircuit of at least one shunt resistor 19 and the vacuum-tube switch 13with the load conductor. The switch contact 12 itself is connected inseries through the second vacuum-tube switch 14 and the thirdvacuum-tube switch 23 and with the contact blade 18 fixed thereto to theconductor 7 and thus also to the load.

The two-arm lever 27 has a roller 25 which rides on the cam rail 5 andis deflected by its edge; the two-arm lever 27 is thus pivoted about itsaxis 271 and thereby actuates through the connection 272 the actuationlever 273 of the second vacuum switch 14. Simultaneously the actuationedge 274 engages against a corresponding actuation edge 294 of thesecond two-arm lever 29 which is thus also pivoted about its axis 291and actuates via the connection 292 the further actuation lever 293 ofthe third vacuum switch 28. As a result of the space between thesurfaces 274 and 294 of the levers 27 and 29 the actuation of the secondvacuum switch takes place shortly before the actuation of the thirdvacuum switch 28 as shown in FIG. 7.

In general the following current path is created in the load branch:From the contact part 2.2 of the fixed step contact 2 via the switchingcontact 12, a conductive connecting part 30, the third vacuum switch 28,thence via a flexible conductive bridge 31 to the second vacuum switch14, from there finally via the conductor blade 18 to the load rail 7 ofthe load line. This is particularly well shown in FIG. 13.

During a load switchover the preselecting auxiliary contact 10 movesfrom n to (n+1) according to the desired switch path. When the auxiliarycontact 10 is in the new position the driven part 11 is released; itstarts its jump and the following switching steps are completed:

1. The first vacuum-tube switch 13 closes the current path,

2. the second and third vacuum-tube switches 14 and 28 switch off thecurrent path from the load branch n to the load conductor,

3. the switch contact 12 moves from n to (n+1),

4. the second and third vacuum-tube switches 14 and 18 switch the loadcurrent path (n+1) to the conductor to complete the switchover,

5. the first vacuum-tube switch 13 switches back to the startingposition.

FIG. 14 shows a single fixed contact 2 which is generally U-shaped andhas two parallel contact legs 41 and 42 which extend parallel to eachother and between which is a perpendicular connecting bight 43 which hasmeans 44 to mechanically and electrically connect it to the respectivefixed contact.

FIG. 15 shows the fixed contact shown individually in FIG. 14 with theselector contact bridges K1 and K2 which slide over it and whichconstitute the auxiliary contact 10 and the switch contact 12 of FIG. 9.

We claim:
 1. In combination with a step transformer having a row of contacts including at least a first contact and an adjacent second contact, a step switch comprising:a drive shaft extending along the row of transformer contacts; a support movable relative to the drive shaft along the row of transformer contacts; a fixed contact fixed on the support and movable therewith along the row of transformer contacts to successively engage same; a buss conductor; a switch connected between the fixed contact and the buss conductor; first means for slowly displacing the support in one direction along the row for displacement of the fixed contact from the first contact to the second contact and in the opposite direction along the row for displacement of the fixed contact slowly in the opposite direction from the second contact to the first contact; a movable contact movable relative to the support and along the row of transformer contacts; a switch connected between the movable contact and the buss conductor; second means including a force-storage unit connected between the movable contact and the drive shaft for, on movement of the fixed contact from the first contact to the second contact, rapidly displacing the movable contact from the first contact to the second contact once the fixed contact is moved fully to the second contact and on opposite movement of the support by the shaft for, on movement of the fixed contact from the second contact to the first contact, rapidly displacing the movable contact from the second contact to the first contact once the fixed contact is moved to the first contact.
 2. The step-transformer switch defined in claim 1 wherein each of the switches is a vacuum switch.
 3. The step-transformer switch defined in claim 2, further comprisinganother vacuum switch connected in series between the buss conductor and the switch of the movable contact; and means for generally simultaneously actuating the series-connected vacuum switches between the buss conductor and the movable contact.
 4. The step-transformer switch defined in claim 1 wherein the row extends longitudinally and each transformer contact has two transversely spaced parts respectively engageable with the movable and fixed contacts.
 5. The step-transformer switch defined in claim 1 wherein the drive shaft is threaded into the support carrying the fixed contact, the switch further comprisinga slide carrying the movable contact and movable along the row independently of the fixed-contact support and connected via the force-storage unit with the fixed-contact support.
 6. The step-transformer switch defined in claim 5 wherein the second means includesa latch for arresting the movable contact against movement along the row from the second contact to the first contact until the fixed contact has moved all the way from the second contact to the first contact and for thereupon releasing the movable contact to jump from the second contact to the first contact and vice versa on movement of the fixed contact from the first to the second contact.
 7. The step-transformer switch defined in claim 4 wherein the switches are carried on the support and the conductor buss conductor is a main conductor buss conductor and is fixed relative to the transformer contacts, the step switch further comprising:an auxiliary conductor buss conductor carried on the support, the movable contact riding on the auxiliary conductor buss conductor.
 8. The step-transformer switch defined in claim 4 wherein each transformer contact is generally U-shaped.
 9. The step-transformer switch defined in claim 1 wherein the force-storage unit includes a spring braced between the support and the movable contact.
 10. The step-transformer switch defined in claim 9 wherein the spring surrounds the spindle.
 11. The step-transformer switch defined in claim 1 wherein the movable contact is carried on and movable relative to the support.
 12. The step-transformer switch defined in claim 1, further comprising:a pair of fixed cams extending longitudinally along the rows; and switch actuating means carried on the support and engaging the cams for operating the respective switches.
 13. In combination with a step transformer having a row of contacts including at least a first contact and an adjacent second contact, a step switch comprising:a threaded drive shaft extending along the row of transformer contacts; a support movable relative to the drive shaft along the row of transformer contacts and threaded on the drive shaft; a fixed contact fixed on the support and movable therewith along the row of transformer contacts to successively engage same; a buss conductor extending longitudinally along the row of transformer contacts; a vacuum switch connected between the fixed contact and having an output riding on the buss conductor; first means for rotating the shaft and slowly displacing the support in one direction along the row for displacement of the fixed contact from the first contact to the second contact and in the opposite direction along the row for displacement of the fixed contact slowly in the opposite direction from the second contact to the first contact; a slide movable relative to the drive shaft and to the support; a movable contact carried on the slide; a switch and a resistor connected between the movable contact and the buss conductor; second means including a spring-loaded force-storage unit braced between the slide and the support for, on movement of the fixed contact from the first contact to the second contact, rapidly displacing the movable contact from the first contact to the second contact once the fixed contact is moved fully to the second contact and on opposite movement of the support by the shaft for, on movement of the fixed contact from the second contact to the first contact, rapidly displacing the movable contact from the second contact to the first contact once the fixed contact is moved to the first contact. 